Method of and apparatus for interrupting electric arcs



V. GROSSE June 17, 1941;

METHOD OF AND APPARATUS FOR INTERRUPTING ELECTRIC ARCS Filed Jan. 4, 1939 75 Vacuum Pump Una 50m Source of F/u/d Pressurw Inventor:

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Vitaly by cu) is Attorney.

Patented June 17, 1941 METHOD OF AND APPARATUS FOR INTER- RUPTING ELECTRIC ARCS Vitaly Grosse, Berlin-Lichterlelde, Germany, assignor to General Electric Company, a corporation of New York Application January 4, 1939, Serial No. 249,304 In Germany January 10, 1938 Claims.

My invention relates to a method 0! and apparatus for interrupting electric arcs, more particularly alternating current power arcs, and has for its principal object the provision of an improved method of and apparatus for are interruption for eil'ecting appreciable reduction in the amount of are energy so as to facilitate final extinction of the arc.

Electric circuit interrupters, and particularly heavy duty breakers for alternating current power circuits, are subjected to great thermal and mechanical stresses when the are energy generated during the interrupting process is high. It has been proposed to limit the arc energy, 1. e., the heat generated during arcing, by confining the arc within a short gap coincident with the application of an extinguishing agent, such as a fluid blast. However, in the case of high voltage power arcs, this method introduces another problem, that of restriking of the arc, due to the comparatively low dielectric strength of a short gap. Furthermore, in the case of gas blast circuit breakers, counter-pressures are developed at the arc which necessitate an increase in blast pressure and therefore in the work requiredto eiiect arc interruption.

In accordance with the present invention, these disadvantages are overcome by greatly reducing the amount of are energy irrespective of the length of the arc and the magnitude of the arc current by causing the arc to be formed in air at greatly reduced pressure or a gaseous medium having a low ionization potential as compared with air at atmospheric pressure. The are extinguishing process is thereby greatly facilitated by this preliminary step of reducing the arc energy.

By way of example, the arc cah be drawn in a gaseous medium of low density, such as for example air at a pressure approximately .05 to .10 atmosphere. As the arc is formed in this rarified atmosphere, the arc energy is greatly limited so that suitable extinguishing means can be applied at the most favorable time for arc interruption, which in the case of an alternating current arc is substantially at or somewhat in advance of the current zero.

The reduction in are energy is accomplished by reducing the arc voltage, which comprises essentially two components, the voltage drop across the arc column and that at theanode and cathode. By reducing the density of the surrounding gas, or by using a gaseous medium with a particularly low ionization potential, such as metallic vapors for example, the column voltage drop can be greatly reduced. In the case of ordinary switch contacts, I have found it preterable to limit the gas pressure to approximately .05 to .10 atmosphere, depending upon the nature of the gas used, since at very low pressures the voltage drop at the anode and cathode increases.

However. very. low pressures can be used, if desired, by constructing the electrodes of suitable materials that are well known in the gas discharge tube art for limiting the potential drop at the electrodes. By way of example thoriated tungsten, etc., are electrode materials that can be used for reducing the voltage drop at the electrodes.

My invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part oi. this specification.

Referring to the drawing, Fig. 1 is an elevational view, partly in section, of an electric circuit breaker embodying the present invention; Fig. 2 is a similar view showing a part of the breaker of Fig. 1 in the open circuit position; Fig. 3 is an elevational view, partly in section, oi. another form my invention may assume, and Fig. 4 is a sectional plan view of the apparatus shown by Fig. 3.

The circuit interrupter illustrated by Fig. 1 comprises relatively movable contacts i and 2 that are arranged to separate within an insulating casing 3 forming an arc chamber. The contact I is shown as fixed at one end of the arc chamber, so as substantially to close the are chamber at that end and the coacting rod contact 2 is suitably mounted for reciprocal longitu dinal movement within the chamber. In the closed circuit position shown, the contacts are in plug and socket relation to establish the circuit between the breaker terminals which can comprise the fixed contact I and a contact member i0 at the opposite end o the arc chamber having a sliding contact engagement with the rod contact 2.

For the purpose of reducing the density of the gaseous medium in which the arc is formed when the contacts i and 2 separate, the arc chamber 3 can be related to suitable evacuating means, such as a vacuum pump of well known construction, or means such as the piston 4 for creating a suction in the space in which the arc is drawn. In the specific construction shown by way of example, the piston 4 is connected to a pair of operating rods 5 that can be through a link 20 to the valve 6.

suitably operated exteriorly of the'arc chamber in a predetermined manner with reference to the contact 2. In such an arrangement thearc chamber 3 is cylindrical in form and the piston 4 is fitted with respect to the cylinder walls so as to produce the desired reduction in pressure in the vicinity of the arc.

During the initial stage of the opening operation, the contact 2 and the piston 4 can move together so that-the arc will be formed within an atmosphere of low density. As previously stated, the construction and speed of operation of the piston 4 "is preferably such that the reduction in pressure is limited approximately to 0.05 to 0.10- atmosphere, depending upon the nature of the gas employed. Although an air circuit breaker is illustrated, it shall be understood that other gaseous mediums, such as carbon dioxide for example, may be employed where desired.

After the above described preliminaryoperation wherein the arc energy is greatly limited due to the surrounding rarifled atmosphere, an arc extinguishing agent is applied suddenly to effect arc interruption. In the present case when the piston 4 has descended to the dottedline position, indicated at 4', the piston motion is arrested and the contact 2 continues its opening movement. In so doing the contact 2 opens a passage 1 communicating with the arc chamber and with a suitable source of fluid pressure indicated at 6. At the instant when the passage 1 is opened, the fluid under. pressure, which in the present instance is air or a suitable arc extinguishing gas, passes through the control valve 6' and flows at high velocity through the arc path into the chamber to extinguish the arc.

Ifhe main circuit, which is suitably connected to the breaker terminals at I and i is accordv ingly interrupted.-

Preferably the piston operating rods 5 and the rod contact 2 are related by suitable means so that the contact 2 opens the passage I ator slightly in advance of a current zero in the case of an alternating current arc. Zero selector means are known in the circuit breaker art, and since they form no part of the present invention illustration thereof is omitted in the interest of clearness. It will also be apparent that the stroke of the piston 4 can be regulated so that the extinguishing agent is applied when the arc reaches a predetermined length that is most favorable for arc extinction. By way of example, a simple operating arrangement is shown for controlling the movable contact 2, the piston 4 and the valve 6' in accordance withthe present invention. The main operating .shaft at 2a represents the actuating member of conven tional operative mechanism for opening and closing the breaker. The shaft is operatively related through a crank 21 to the contact extension 2 such as by a sliding connection, and The piston rods 5 are biased into following engagement with the extension 2 "by springs 5', and'contact 2 is biased open by spring 2". Therefore, as the crank 2b is rotated clockwise by the actuating shaft 2a to open, the breaker, the piston 4 moves downward with'the contact 2 by reason of the springs 5' and 2.". When, however, the contact reaches a predetermined position, indicated by dotted lines, the movement of the piston is stopped by the limit members 5 on the piston rods as indicated in Fig. 2 and the port I is uncoveredtogether with opening of the valve 6' for applying the extinguishing fluid to the arc chamber. In closing, the crank is rotated counter clockwise to compress the springs 5' and 2" and raise the piston 4 and contact 2 to the closed position shown.

In the case of small capacity circuit breakers, it will be apparent that the special source 6 can be omitted so that th breaker functions by autobla'st. That is, the piston 4 as it reduces the pressure in the arcing space also compresses the air at the lower part of the chamber during the initial circuit opening movement so that a blast is produced after predetermined lengthening of the are when the port I is'uncovered.

As the gas blast is suddenly admitted to the arc chamber, the arc voltage rises almost instantaneously to a multiple of the value in the rarified space, and extinction of the arc takes place at the next passage of the arc current through zero.

In order to enable the extinguishing medium to flow from the arc chamber after application of the gas blast, the chamber can be conveniently provided with a non-return valve suitably constructed for high speed operation. Such a valve is shown at 8 for closing the arc chamber at 8'. When the pressure within the arc chamber due to the arc extinguishing blast overcomes the tension of the biasing spring 8", the valve is opened at high speed by reason of the large working area that is efiective after a very small initial opening at 8. The valve of course remains seated during the initial circuit opening stroke when the gas pressure in the arcing space is temporarily reduced. The valve 8 is reciprocally guided by ribs 9 arranged within the annular exhaust passage so as to afford minimum [resistance to fluid flow.

vFig. S illustrates such an arrangement wherein the contacts I and 2 separate within an arc plurality of short arcs in series. The chamber 3 can be connected at 12 to a vacuum pump for effecting the desired reduction in pressure. A magnetic blow-out device of well known construction is indicated at l3 for urging the arc lat-' erally between the metal plates. The pole pieces of the magnetic blow-out device are indicated at [4.

A further means for causing the arc to form between the plates comprises an insulating tip l5 of suitable arc resisting material carried at the end of the contact 2 for substantially filling the space previously occupied by the rod contact, as the opening movement progresses. As in the previous instance the arc is caused to form within a rarified atmosphere so as to reduce the arc energy, and a separate extinguishing agent or means is applied to efiect final extinc tion of the arc.

It shall be understood that my invention is not limited to the specific types of circuit interrupters herein described and illustrated and that the main concept of facilitating arc interruption by greatly reducing the are energy in a medium having a low ionization potential can be applied to other types of circuit inter rupters.

It should also be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

What I claim as new and desire to secure by Letters Patent 0! the United States is:

1. The method of interrupting an electric power arc which comprises reducing the gas density an appreciable extent in an arc chamber, forming the arc in said chamber so that the are energy is largely reduced as the arc is initially formed and subsequently applying a fluid blast to said are after predetermined lengthening of said arc.

2. An electric circuit interrupter comprising are forming means, an arc chamber in which the arc is initially drawn, means for ,at least partially evacuating said chamber in accordance with the arc formation so that the energy oi the initially formed arc is largely reduced, and means for directing a gas blast through the arc only subsequent to predetermined formation thereof.

3. An electric circuit breaker comprising relatively movable contacts, an arc chamber within which the arc is formed upon separation of said contacts, piston structure operable within said chamber for appreciably reducing the gas density in the space in which said arc is formed during initial arcing, one oi said contacts being operatively related to said piston structure so as to close said chamber during initial formation of said are and for subsequently opening said chamber, and means for directing a gas blast through said opening into said chamber to extinguish the are.

4. An electric circuit breaker comprising relatively movable contacts, an arc chamber 'in which the arc is formed upon separation of said contacts, a piston operatively connected to one of said contacts for reducing the gas density in said chamber in accordance with initial arcing upon contact separation, a non-retum valve arranged to close said chamber when the pressure therein is substantially equal to or less than atmospheric, said piston having an openingnormally closed by said related contact except after predetermined separation 01 said contacts. and means for directing gas under pressure through said opening into said chamber to extinzuish the arc.

5. An electric circuit breaker comprising relatively movable contacts, an arc chamber in which the arc is formed upon separation of said contacts, means for appreciably reducing the gas density in said chamber during initial arcing, and means for opening said chamber after formation oi! said are for introducing a gas'blast into the arc path.

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